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Clones of Dolly the sheep are ageing normally

The iconic farm animal's legacy lives on in a flock of clones which, unlike her, appear to be healthy in their old age.

Nottingham Dollies show that cloned sheep can live long and healthy lives.

The University of Nottingham

Clones of the Dolly the sheep – the first mammal cloned from an adult, non-reproductive cell – have aged normally, according to a report by researchers in the UK and Mexico.

Some 13 cloned sheep, including four created from the same genetic material as Dolly dubbed the "Dollies", were monitored when they were seven to nine years old. They were all found healthy, with normal blood pressure and no metabolic diseases.

The worst seemed to be mild (or, in one case, moderate) osteoarthritis.

The work, published in Nature Communications, is the first long-term study of the health effects of cloning in a large animal.

Some 20 years ago, University of Edinburgh biologist Keith Campbell was instrumental in Dolly's creation. The sheep ended up with three "mothers" of sorts – one provided the egg, another DNA from a mammary cell and the third carried the embryo to term – and she was born on 5 July 1996.

But she died relatively young, euthanised five months shy of her seventh birthday due to severe osteoarthritis. Her early death, at about half of her breed's lifespan, raised concerns that cloned animals didn't age normally.

A few years after Dolly's birth, Campbell moved to the University of Nottingham, where he continued his work, cloning more sheep – some identical to Dolly and others of different breeds.

Campbell died in 2012, but Kevin Sinclair, a colleague of Campbell's at the University of Nottingham, took over his flock.

In 2015, the cloned sheep underwent a series of comprehensive assessments for obesity, high blood pressure and osteoarthritis – three major medical conditions in aged human populations.

MRI and X-ray scans showed they were ageing normally with no signs of diabetes or high blood pressure.

While the team couldn't compare the cloned sheep with normal animals of exactly the same breed and age, and did not measure molecular markers associated with ageing, they write the study supports the "emerging consensus" that cloned animals are "healthy and seem to age normally".